The invention relates generally to a monitoring system rendering a synthetic display derived from multiple cameras mounted at various locations, and more particularly, to alerting a viewer on special situations observed.
Video monitoring systems are well known. In the case of vehicles, several types of monitoring systems are in use. Some vehicles, e.g., busses, have cameras mounted so that the driver can view road areas beside or behind the bus. However, there is typically only one camera, and the display merely shows exactly what the camera sees. There is no attempt to analyze the displayed image. These systems simply act as viewing mirrors for hard-to-see areas. Similarly, law enforcement vehicles may capture a historical record of the view from the front window.
Some vehicles, such as computer controlled cars, also include sensors. The sensors detect potentially dangerous situations, such as, closing-up too rapidly on another vehicle. A variety of sensors have been used, for example, sonar, lasers, and microwaves. These systems do not provide a general situation display, rather they merely detect a few dangerous situations.
Radar and sonar systems can produce a situation display, and sometimes do some amount of analysis, for example, as in an air traffic control system. However, radar and sonar systems are not based on video images, but rather on the processing of reflected signals transmitted at specific frequencies.
Several types of surveillance systems are known. Typically, the systems route multiple video streams to a central location. The video streams can be displayed on corresponding monitors. If the number of cameras is greater than the number of display stations, then the system usually displays camera views in sequence, or on operator demand. These type of systems do not perform analysis, nor do these systems merge multiple streams into a single situation display. At most they may tile multiple independent views on a single screen with time and location annotations.
There are also systems that monitor specific places, such as escalators, elevators, toll gates, bank machines, and perimeter fences, in order to determine the occurrence of particular situations. Some of these systems may attempt to analyze the video in order to detect moving objects, for example, to extract a license number. However, these system typically do not combine information from multiple sources, nor do they generate an overall situation display, nor synthesize an image from a different point of view.
The invention provides a situation awareness system which includes a plurality of cameras. Each camera acquires a sequence of images of overlapping parts of an area of interest. An analyzer merges the sequences of images acquired by the plurality of cameras, and identifies moving objects in the area of interest. A display device displays the merged sequences of images, and information associated with the identified moving objects.
In one aspect of the invention, the optical flow in temporally successive images of a single video stream are analyzed to generate motion fields. Spatially adjacent images of multiple video stream are registered to obtain depth images. The motion fields and depth images are segmented to generate partially attributed data objects. Using an application specific database and analysis, the partially attributed data objects are converted to fully attributed data objects and events which are displayed as annotated graphic elements and alerts. As one feature of the invention, the viewing orientation of the display is independent of the point of view of the cameras.